1. The Field of the Invention
This invention relates to semiconductor devices upon a semiconductor substrate as they are electrically connected to each other to complete integrated circuits. More particularly, the invention relates to semiconductor devices upon a semiconductor substrate having electrical connections with the property of high-temperature (ie. above about 70.degree. K) superconductivity.
2. The Relevant Technology
Semiconductor processing involves a number of different chemical and physical steps whereby minute electronic devices are created on a substrate at the front end of a fabrication process. Integrated circuits are constructed using multilayers of interrelated patterns of various materials, the layers being created by such processes as chemical vapor deposition (CVD), physical vapor deposition (PVD), and epitaxial growth. Some layers are patterned using photoresist masks and followed by wet and dry etching techniques.
Patterns are created within layers by the implantation of dopants at particular locations. The substrate upon which the devices are created may be silicon, gallium arsenide, glass, or other appropriate material.
In the production of integrated circuits upon semiconductor wafers, the back end of production involves connecting all the fabricated semiconductor devices on the chip with electrically conductive materials. This back-end-of-line (BEOL) "wiring" step, which is the electrical connection scheme for connecting semiconductor devices, completes the circuits as designed to function within the total integrated circuit device. Metal lines are used in the metallization process as electrical connections between semiconductor devices.
Several technical challenges arise for back-end wiring as more complex integrated circuitry is increasingly miniaturized upon semiconducting dies. One problem is Joule heat generation caused by resistive current flow through the metallization or wiring. A side-effect of heat generation due to resistive current flow is electromigration of certain preferred electrical conductors such as aluminum and copper. Electromigration is the diffusion of atoms in electric fields in the metal wiring that results in wire thinning and ultimate breach and failure after it has been put into service. Such a phenomenon eventually opens the circuit by breaking the metal line and the device fails. A second heat problem is the side effect of device failure from overheating. Because heat is a product of the resistive-current flow process, a device with inadequate heat removal abilities causes the device to inadequately reject heat until resistivity increases to the point of device failure. The system can recover by shutting down and allowing the whole system to cool. Valuable time, however, is lost, a process controlled by the device runs without control, or information is lost.
Another problem is capacitance build-up between metallization lines that are separated by dielectrics. The need for ever-decreasing dielectric layer thicknesses makes capacitance build-up more likely as the distance between metal lines decreases. Undesired capacitance build-up creates unwanted electronic phenomena within the integrated circuit called cross-talk that causes marginal device function or device failure.
Yet another problem is the ever-decreasing metal line width requirement that makes metallization by photolithographic and sputtering techniques more difficult to achieve. As sub-tenths of micron line widths are being attempted, a technique for achieving thinner but continuous and adequately conductive metal lines is required.
The initial scientific breakthroughs in the superconductor art more than a decade ago were with 123 YBaCuO.sub.x compounds, but since their discovery, several higher-temperature superconductors have been developed such as REBaCuO.sub.x, 2223 BSCCO (Bismuth-Strontium-Calcium-Copper oxide), and Thallium-Bismuth-Lead copper oxides among, others. Superconductors have the advantage of low resistance conduction of electricity.
It would be an advantage in the semiconductor art to use the low resistance of superconductors in the metallization process of semiconductor device fabrication.